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■ «|L Agriculture 
I t Canada 



Research Direction generale 
Branch de la recherche 



Contribution 1983-27E 



Climatic zonation for 
forage crops in the 
Atlantic Region 




Canada 



The map on the cover has dots representing 
Agriculture Canada research establishments. 



Climatic zonation for 
forage crops in the 
Atlantic Region 



A. BOOTSMA 
Agrometeorology Section 
Land Resource Research Institute 
Ottawa, Ontario 

LRRI Contribution No. 83-01 



Research Branch 
Agriculture Canada 
1984 



Copies of this publication arc available from: 

A. Bootsma 

Agrometeorology Section 

Land Resource Research Institute 

Research Branch, Agriculture Canada 

Ottawa, Ontario 

K1A0C6 

Produced by Research Program Service 

©Minister of Supply and Services Canada 1984 

Egalement disponible en francais sous le titre 

Zonage climatologique pour la culture de.s plantes fourrageres 

dans la region de I'Atlantique 



TABLE OF CONTENTS 

Page 

ACKNOWLEDGEMENTS iv 
SUMMARY, RESUME v 

1. INTRODUCTION 1 

2. METHODOLOGY 3 

2.1 Estimating maturity dates for first cut 3 

2.2 Estimating the critical fall harvest period 

for alfalfa 6 

2.3 Zonation criterion for harvest frequency 

and potential yield 8 

2.4 Zonation criteria for drying index and 

water deficits 8 

2.5 Mapping procedures 12 

3. RESULTS AND DISCUSSION 12 

3.1 Heat unit zonation for estimating optimum first 
harvest date 14 

3.2 Critical fall harvest period for alfalfa 16 

3.3 Zones for harvest frequency and potential 

yield 19 

3.4 Drying index and water deficit zonation 23 

4. CONCLUSION 30 

5. REFERENCES 31 

6. APPENDIX 35 



ii 

LIST OF TABLES 



Page 



1. Estimated growing degree-day requirements for 
specific maturity stages in several forage crops. 4 

2. Equations for calculating water deficits (WD) from 
Accumulated Potential Water Loss (APWL). 12 

3. Average dates of accumulated growing degree-days 

(GDD) for maturity zones in Figure 5. 16 

4. Critical fall harvest period for alfalfa for zones 

in Figure 6. 18 

5. Growing season length criterion for zones in Figure 

7. 19 

6. Estimated optimum harvesting frequencies of several 
forage species for each zone in Figure 7. 21 

7. Estimated average potential dry matter yields of 
several forage species for each zone in Figure 7. 22 

8. Range in drying indices for zones in Figure 8. 25 

9. Range in Accumulated Potential Water Loss (APWL) 

and water deficits for zones in Figure 9. 26 

10. Qualitative comparison between water deficit zones, 
Canada Soil Climate Map moisture classes and 

moisture stress on two forage species. 29 

11. List of climatic stations used in zonation study 

and derived data. 38 



Page 



111 
LIST OF FIGURES 
Figure 

1. Correction factor for monthly growing degree-days 
above 5°C (GDD) in spring. 6 

2. Correction factor for monthly growing degree-days 
above 5°C (GDD) in autumn. 7 

3. Relationship between Thornthwaite Water Deficit and 
Accumulated Potential Water Loss at three soil 

water holding capacities. 11 

4. General map of the Atlantic region study area. 13 

5. Maturity zones for first cut of forage crops. 15 

6. Zones of critical fall harvest period for alfalfa. 17 

7. Zones of growing season index for cutting 
frequencies and potential yields of forage crops. 20 

8. Drying index zones for hay-making. 24 

9. Water deficit zones for forage crops. 27 

10. Approximate location of climatic stations used in 
forage crop zonation study. 37 



ACKNOWLEDGEMENTS 

This climatic analysis of the Atlantic region is part of an attempt to 
divide the region into zones for forage crop production and management 
recommendations. Considerable guidance to the work was provided by an ad 
hoc committee on forage crop zonation for the Atlantic region, which 
consisted of Dr. M. Suzuki, Charlottetown Research Station, Mr. J. 
MacMillan, New Brunswick Department of Agriculture and Rural Development 
and the author. Many helpful comments on the work were received from 
members of the Atlantic Advisory Committees on Forages and on 
Agrometeorology , for which the author is grateful. Special thanks are also 
due to Dr. J. Dumanski, Land Resource Research Institute, Mr. W.J. 
Blackburn and J. A. Dyer, both from the Crop Production Division, Regional 
Development Branch and Dr. M. Suzuki for reviewing the manuscript. 

The helpful advice of Mr. D. Grimmett, Charlottetown Research Station 
in computer data processing techniques is acknowledged. Assistance was 
also provided by data processing staff of the Agrometeorology Section, Land 
Resource Research Institute. Some preliminary analyses for this project 
were carried out with assistance from Mr. D.B. Walker and Mr. G.S. Rodd 
while the author was employed by the P.E.I. Department of Agriculture and 
Forestry. Finally, thanks are due to stenographic staff of the Land 
Resource Research Institute for typing services rendered. Cartographic 
work was performed by the cartography unit of the Land Resource Research 
Institute. 



SUMMARY 

This bulletin describes the spatial variation of several derived climatic 
parameters of importance to forage crop production and management in the 
Atlantic Provinces. Accumulated growing degree-days above 5°C (GDD) in spring 
are used to estimate important maturity stages in several forage species for 
first cut. GDD's remaining in the fall are used to indicate probable 
variation in the critical fall period during which alfalfa and possibly other 
species susceptible to winterkill should not be harvested. The length of 
season between specified GDD's accumulated in spring and remaining in fall is 
used as a criterion for designating variation in suitable cutting frequencies 
of forages. Simplified moisture criteria based on rainfall and estimated 
potential evapotranspiration are used to describe regional differences in 
hay-making conditions and in the likelihood of moisture stress during summer 
months. 



RfiSUMfi 

Dans le present compte rendu, nous decrivons la variation en fonction de 
l'espace de plusieurs parametres climatiques influant sur la production et la 
regie des cultures fourrageres dans les provinces de 1' Atlantique. D'apres le 
nombre total de degres-jours de croissance au-dessus de 5°C (D.J.C.) accumules 
au printemps, on a estime a quel moment les cultures de plusieurs especes 
fourrageres sont parvenues au stade de maturation crucial pour la premiere 
recolte. Les D.J.C. qui restent en automne indiquent la variation probable de 
la periode critique automnale durant laquelle la luzerne et certaines autres 
especes sensibles au froid d'hiver ne devraient pas etre recoltees. La 
longueur de la periode entre la date au printemps ou un nombre precis de 
D.J.C. sont accumules et la date en automne ou un nombre precis de D.J.C. 
restent a venir sert de critere pour determiner la variation de la frequence 
appropriee des recoltes de plantes fourrageres. Pour decrire les variations 
regionales des conditions de fenaison et des risques de penurie d'eau durant 
l'ete, on se sert de criteres d'humidite simplifies, base sur l'abondance des 
precipitations et la valeur approximative de 1 'evapotranspiration potentielle. 



1. INTRODUCTION 

The climatic analyses described in this bulletin were undertaken in 
response to a need to divide the Atlantic region into different zones for 
the purpose of making specific recommendations on forage crop production 
and management. Climate has an important effect on the adaptability of 
various forage species and cultivars to the region. Conditions permit a 
wide variety of forage crops to be grown (Atlantic Field Crops Committee 
1980). While timothy is the most widely grown forage grass, other species 
such as orchardgrass and bromegrass are also being cultivated. Legumes 
such as alfalfa, clover, and birdsfoot trefoil are also grown, but 
successful production depends upon good winter survival. In recent years 
annual ryegrass has also increased in popularity as a source of feed. 
Although there are many factors which affect production and management of 
forage crops, climate is one of the most important. The climate not only 
affects growth patterns, persistence, quality and yield, but also 
influences the response of each cultivar to different management practices. 

This study focuses on four main areas in which climate has a 
significant influence. These areas are (i) the time when optimum maturity 
for first harvest is reached, (ii) the critical fall period when alfalfa 
should not be harvested for good management, (iii) the harvest frequency 
and yield of forage crops as influenced by season length and, (iv) 
hay-making conditions and soil water deficits during the summer period. 

(i) The time when forage crops reach specific stages of maturity is an 
important factor in production of high quality forages in the 
Atlantic region. Research has demonstrated that grasses must be 
harvested at early heading and legumes no later than early flowering 
to achieve maximum yield of digestible nutrients (Atlantic Field 
Crops Committee, 1980). It has also been shown that the harvest 
season for timothy can be spread out by planting cultivars that grow 
and develop at different rates and in this way allow the crop to be 
cut at the optimum stage of growth (Grant and Burgess, 1978). The 
date that a particular cultivar will reach the required stage of 
maturity will vary depending mainly upon climatic conditions in the 
region where it is grown. In this study, the average dates when 
cultivars of alfalfa, timothy, and red clover reach specific stages 
of maturity for first cut are estimated on the basis of accumulated 
growing degree-days above 5°C (GDD) in each area. 

(ii) The probable variation in the critical fall period during which 
alfalfa should not be harvested is also examined. Alfalfa must be 
hardened during the fall period to aid survival over winter in many 
parts of North America. Grazing or cutting of alfalfa should be 
avoided for approximately six weeks in the fall because defoliation 
during this period will interfere with the hardening process and will 
increase the chance of winter injury (Fulkerson, 1974; Gottfred, 
1980; Heinrichs, 1969; Woolley and Wilsie, 1961). The period 
required for alfalfa to attain adequate cold resistance will vary 
depending upon climatic conditions. Fulkerson (1970) found that in 



southern Ontario, the harvest date which resulted in the greatest 
decline in alfalfa yields coincided closely with the 25 percent risk 
date of frost in each region. Management recommendations advise 
farmers in Ontario not to cut alfalfa for a six week period centred 
around this critical fall harvest date (Ontario Field Crops Research 
Committee, 1981). Woolley and Wilsie (1961) questioned the validity 
of using the first killing frost to determine the date of fall 
removal, and proposed a system of cold unit accumulation based on 
soil temperature to determine time required for adequate hardiness. 
In the Atlantic region of Canada, it has been observed that alfalfa 
harvested or grazed in the previous fall sustained more winter injury 
(MacKenzie and Suzuki, 1978; Suzuki and McRae, 1979; Willis and 
Suzuki, 1971) . Although proper management does not guarantee 
successful winter survival, it will reduce the risk of winter 
injury. Therefore, crop recommendations state that alfalfa should 
not be cut or grazed between September 1 and October 15 (Atlantic 
Field Crops Committee, 1980). In this study, the critical fall 
period during which alfalfa should not be harvested was defined on 
the basis of accumulated GDD remaining in the fall. This was 
considered a suitable criterion since experience in other regions 
has shown that the critical harvest period is advanced in areas which 
experience an earlier decline in temperature in autumn (Fulkerson, 
1970; Woolley and Wilsie, 1961). 

(iii) The frequency of harvesting and the potential yield of several forage 
species are related to the number of days between the time when 350 
GDD are accumulated in spring and 450 GDD are remaining in fall. 
This criterion is based on the assumption that temperature is a prime 
limiting factor in growth in spring and fall, while during summer 
months growth is mainly a function of time and less influenced by 
temperature (assuming no severe moisture stress) . Potential yield in 
this study is defined as the yield which can be achieved with good 
management under present technology, as approximated by yields 
recorded at research station trials in the region in years with 
relatively good winter survival. 

(iv) The Atlantic region usually receives sufficient rainfall to maintain 
crop growth during summer months. Nevertheless, in some years, 
moisture stress significantly retards the growth of forages (Atlantic 
Field Crops Committee, 1975; Black, 1978; Calder and Nicholson, 
1970) . Regrowth after defoliation during summer months is affected 
most often since moisture stress is most likely during this period. 
For example, dry summer weather in Prince Edward Island in 1975 
prevented a second cut of timothy and reduced the yield of the second 
cut of alfalfa by at least fifty percent (Atlantic Field Crops 
Committee, 1975). A surplus of moisture in summer may also be 
detrimental to forage production in some years or regions. Black 
(1978) observed that an excessive moisture supply caused a decline in 
pasture production, possibly due to waterlogging of soils and 
leaching of nutrients. More importantly, excess moisture during the 
haying season can result in a serious decline in hay quality by 



3 

delaying the harvest past the time when the forage crop is at its 
optimum maturity. Wet weather also causes a serious decline in both 
the quantity and quality of forages after cutting (Wilkinson, 1981). 
The above evidence confirms the importance of moisture status during 
summer months in forage zonation. In this study, spatial variations 
in indices of hay-drying conditions and soil water deficits are 
analyzed, based on potential evapotranspiration estimates and 
rainfall for the period of June through August. Moisture deficits 
are a function of climate (rainfall, evaporation), soil (water 
holding capacity, drainage) and crop characteristics (transpiration, 
rooting habit, drought resistance). Information is incomplete on the 
relationship between all these factors in the Atlantic region and 
therefore simplifying assumptions were made in the analyses. 

This bulletin describes in detail the methods used to assess the 
spatial distribution of climatic parameters recognized as being important 
to forage production and also presents the results of the analyses. The 
information will help agronomists formulate forage production and 
management recommendations for the region. The results also have 
significance for land evaluation and assessment of crop production 
potential. Maximum benefit will be achieved if the climatic information is 
integrated with data on soils in the region. 



2. METHODOLOGY 

2 .1 Estimating maturity dates for first cut 

There is very little information available in the literature on 
suitable methods for predicting stages of maturity in forage crops, even 
though the influence of temperature on development of grasses and legumes 
has been investigated extensively (Knight and Hollowell, 1958; Kozumplik 
and Christie, 1972; Pearson and Hunt, 1972; Smith and Jewiss, 1966). Most 
studies have demonstrated that, except for extremely high temperatures, the 
rate of development to maturity increases with increasing temperature. 
Factors such as moisture, fertility, and daylength may influence the rate 
of development to some extent. However, under cool, moist conditions 
typically experienced during spring in the Atlantic region, temperature is 
the most important factor determining when stages of maturity will be 
reached. Selirio and Brown (1979) used an accumulation of 550 ODD as an 
estimate of the time when alfalfa reaches the flowering stage in southern 
Ontario. Comparison of accumulated GDD with crop maturity stages recorded 
in forage trials conducted by the Atlantic Advisory Committee on Forage 
Crops indicated that in the Atlantic Region, the early bloom stage of 
Saranac and Iroquois alfalfa in post-seeding years is reached when 
approximately 450 GDD have accumulated (Bootsma, unpublished 
observations) . While the early alfalfa cultivars such as Saranac exhibit 
more rapid growth in spring than medium cultivars such as Iroquois, most 
cultivars reach maturity at approximately the same time. The data also 
indicate that Champ timothy reaches the 50 percent heading stage when 



approximately 450 GDD have accumulated. Clair timothy reaches 50 percent 
heading about 50 to 70 degree-days sooner than Champ, and Climax is about 
50 to 70 degree-days later. Clair, Champ, and Climax are timothy cultivars 
recommended for production in the region that are rated as very early, 
early, and medium maturity respectively. Double cut red clover cultivars 
Ottawa and Lakeland reach the early bloom stage when about 450 GDD have 
accumulated. 

Considerable variation in the degree-day requirement between seasons 
and locations indicates a need to develop a more accurate method of 
predicting maturity. For example, alfalfa grown at St. John's, 
Newfoundland, tends to require fewer heat units to reach the early bloom 
stage than alfalfa grown at warmer Maritime locations. In some years and 
at some locations there is also more spread in maturity dates and 
degree-day requirements between varieties than in other years or at other 
locations. In the absence of an alternative method, the accumulated 
degree-day values listed in Table 1 were used to estimate maturity stages 
in timothy, alfalfa and red clover in spring. These values may need to be 
adjusted in future when more data from experimental plots becomes available. 



Table 1. Estimated growing degree-day requirements for specific 
maturity stages in several forage crops 



Accumulated 
growing degree 
days above 
5°C (GDD) 



Approximate stage of maturity in post-seeding years 



alfalfa* 



red 
clover** 



Clair 



timothy 



Champ 



Climax 



350 
400 
450 
500 



early bud - early head 
late bud - 50% head early head 
early bloom early bloom full head 50% head early head 

full head 50% head 



* average based on Saranac and Iroquois cultivars. 
**average based on Lakeland and Ottawa cultivars. 



Average dates when maturity stages in Table 1 are reached in the 
Atlantic region were estimated by determining the average date when 350 and 
450 GDD have accumulated, using the following quadratic regression 
equations: 



2 

Y = 126.72 - 12.527 X + 0.3077 X (1) 

1 11 

2 

Y = 140.11 - 13.201 X + 0.3354 X (2) 

2 11 

where Y^ and Y2 are the average dates when 350 and 450 GDD 

respectively have accumulated in spring (June 1=1); 
X;l is the mean air temperature for May and June (°C). 

Temperature normals for the 1951-1980 period (Environment Canada, 1982) 
were substituted into these equations to estimate Y^ and Y2 at 231 
climatic stations in the region. Temperature normals for stations with 
less than 20 years of records were previously adjusted to the 30-year 
normal period by Environment Canada using standard techniques. 

Equations (1) and (2) were determined by multiple linear regression 
analyses using data from 68 climate stations in the Atlantic region for the 
1941-1970 normal period (Environment Canada, 197D. Both equations had a 
coefficient of determination (r^) of 0.984 and standard error of estimate 
(s.e.) of 1 day. In developing these equations, accumulated GDD were 
determined from a graph of monthly mean air temperature for each station by 
summing daily GDD values. A regression equation was used to correct GDD 
sums based on the graphs for months with less than 200 GDD as follows: 

Y c = 19.98 + 0.904 Y G (3) 

where Yq is the corrected monthly GDD summation; 

Yq is the monthly GDD sum determined from the mean 
temperature graph. 

Equation (3) was developed using monthly GDD published by Environment 
Canada (Treidl, 1978) for Yq, since these were calculated from daily 
maximum and minimum air temperatures. Data from 23 station-months yielded 
an r 2 value of 0.99 and an s.e. of 6.5 GDD. This method of correcting 
GDD sums calculated from mean air temperatures proved to be as accurate but 
simpler than Thorn's method (1966). A correction factor shown in Figure 1 
was also applied for months with zero GDD but with mean temperatures above 
1°C. Figure 1 was determined from comparisons of mean monthly air 
temperature with GDD published by Environment Canada for station months 
having zero GDD based on the graph method. 

The accuracy using the graph method with corrections to determine dates 
when 350 GDD and 450 GDD have accumulated was further checked by comparison 
with data published by Environment Canada (Treidl, 1979) for 36 locations. 
Weekly GDD summations by Environment Canada were interpolated to derive the 
350 and 450 GDD dates. The results of these two methods were highly 
correlated (r = 0.996) and were generally within 1 day of each other, 
indicating that the graph method was sufficiently accurate for the purpose 
of this study. 



30 


i 


1 i 


i 


1 i ■ 


i 


20 


- 






• / • 


- 


10 


_ 








_ 


n 


• •J 




/• i 


i i 


i 



-20246 
MONTHLY MEAN AIR TEMPERATURE (°C) 



Fig. 1 Correction factor for monthly growing degree-days above 5°C (GDD) 
in spring. 



2.2 Estimating the critical fall harvest period for alfalfa 

The critical fall period during which alfalfa should not be harvested 
was defined as the ^5-day period beginning on the date when an average of 
^50 GDD were still remaining in the fall. This criterion was considered 
appropriate since periods were found to coincide with the critical harvest 
period presently recommended for the Atlantic region (Atlantic Field Crops 
Committee, 1980) for locations where alfalfa field trials have been 
regularly conducted (Charlottetown, Nappan, Truro). Furthermore, periods 
thus defined were centred near the 25 percent risk date for frost in inland 
areas of New Brunswick and Nova Scotia, which corresponded closely with the 
relationship between the critical harvest date (midpoint of the critical 
harvest period) and frost risk in Ontario (Fulkerson, 1970). Tn coastal 
regions, this period was centred considerably earlier than the 25 percent 
risk date due to the moderating influence of ocean waters on night-time 
temperatures. The criterion may need to be modified in future when more 
information becomes available on the effect of cutting management on winter 
survival in the Atlantic region. 



A method similar to that used for estimating ODD in spring was used to 
calculate the average date when 450 GDD were remaining in the autumn. 
Normal temperature data for the 1951-1980 period (Environment Canada, 1982) 
were used from 232 climate stations in the following regression equation: 



x 3 = 



-43.3^ + 6.317 X 



(4) 



where Y3 is the date when 450 GDD are remaining in the fall(August 1=1); 
X is the mean air temperature for September and October (°C). 

Equation (4) was determined by linear regression analyses using data 
from 68 stations in the region for the 1941-1970 normal period (Environment 
Canada, 1971). This equation had an r^ value of 0.98 and an s.e. of 1 
day. Various combinations of average temperature were tried along with 
quadratic terms, but these did not significantly improve the accuracy of 
the regression relationship. The 450 GDD date (Y3) was determined from 
normal temperature graphs by accumulating daily GDD values backwards in 
time from the date when the mean temperature curve dropped below 5°C. 
Similar methods were employed to correct GDD summations as with the spring 
data. The regression equation used to correct GDD sums for months with 
less than 220 GDD was: 



Y c = 24.03 + 0.894 X G 



(5) 



where Yq is the corrected monthly GDD summation; 

Y Q is the monthly GDD determined from the mean temperature graph. 



60 




1 




1 


1 ■ 


1 ' 


1 


- 


40 


- 










• 


• 
• 


- 


20 










• 


/ • 




" 







—J — 


-—0 


. 1. « . 


• y 


1 


1 





-4-2 2 4 

MONTHLY MEAN AIR TEMPERATURE (°C) 



Fig. 2 Correction factor for monthly growing degree-days above 5°C (GDD) 
in autumn. 



Equation (5) was determined by using monthly GDD summations published 
by Environment Canada (Treidl, 1978) for Yq, similar to equation (3) for 
the spring. Data from 26 station-months yielded an r 2 value of 0. Q Q and 
a s.e. of 0.2 GDD. Figure 2 shows the correction factor used for months 
with zero GDD based on the mean temperature graphs, but which have mean 
temperatures above 0°C. This figure is comparable to Figure 1 for the 
spring data. 

The accuracy with which the graph method estimated the date when 450 
GDD remain in fall was evaluated by comparison with dates determined from 
interpolating weekly GDD summations published by Environment Canada 
(Treidl, 1979) for 36 stations. Dates determined from Environment Canada 
data were assumed to be correct values since these GDD summations were 
based on daily maximum and minimum air temperatures. The graph method with 
corrections applied yielded dates which were generally 1 to 3 days earlier 
than dates based on Environment Canada data. The following regression 
equation describes the relationship between dates determined by these two 
methods: 

Y A = 2.96 + 0.954 X G (6) 

where Y^ is the date when 450 GDD are remaining in fall based on 
Environment Canada data; 
X is the date determined using normal temperature graphs with 
corrections applied. 

Equation (6) had an r 2 of 0.97 and a s.e. of 1.3 days. Estimates of 
the 450 GDD date in the fall for all 232 stations in the region were 
adjusted by using the value of Y? in equation (4) for X G in equation 
(0). These adjusted values were taken as the starting date of the 4^- day 
period during which alfalfa should not be harvested. 

2.3 Zonation criterion for harvest frequency and potential yield 

Sections 2.1 and 2.2 describe procedures used to estimate when 3 q GDD 
have accumulated in spring and when 450 GDD are remaining in fall in an 
average year. The number of days between these two dates (DAY?) was 
calculated and used as a zonation criterion for the frequency of harvest 
and potential yield of various forage species. The rationale for using 
this criterion was partly discussed in the introduction. In each 
particular region, perennial forage crops have available for growth the 
number of days given by this parameter plus an additional 800 GDD (in 
spring and fall) . For alfalfa, the parameter DAYS represents the time 
available for regrowth for early cultivars after the first cut until the 
critical fall period when harvesting should be avoided. 

2.4 Zonation criteria for drying index and water deficits 

The relative potential for curing hay in the field in various parts of 
the Atlantic region was assessed by using a drying index developed from 



field experimental data by Hayhoe and Jackson (1974). The index was 
defined as 

I = PE - 0.2 P (7) 

where PE is the potential evaporation (ram); 
P is the precipitation (mm) ; 
I is the index value. 

Equation (7) can be used to obtain daily values of I or an accumulated 
value over a given number of days. For the purpose of this study, the 
accumulated value from June through August was calculated for over 230 
stations using temperature and precipitation normals for the 19 51-1980 
normal period (Environment Canada, 1982). Total PE was estimated using an 
equation developed by Baier and Robertson (1965) and the conversion factor 
determined by Baier (19 71) as follows. 

The average daily latent evaporation (LE) in cnP for the period June 
to August was calculated by the equation, 

LE = -57.334 + 1.6704 TMAX + 1.6794 TRANGE + 0.0486 Q (8) 

where TMAX is the average daily maximum temperature from June through 

August (°C); 
TRANGE is the average difference in °C between the daily maximum and 

daily minimum temperature for the same period; 
Q Q is the average total solar radiation at the top of the 

atmosphere over the same period (cal cm~2 day - -'-) 

Q Q was estimated from station latitude (LAT) using: 

Qo = 934.4 + 3-6308 (52.0 - LAT) ' 927 (9) 

for latitudes between 43°N and 51.5°N, and 

Q = 907.3 + 4.1759 (59.0 - LAT) ' 970 (10) 

for latitudes above 51.5°N and less than 59°N. 

In the development of Equations (9) and (10), Q was calculated at 
specific latitudes using daily values of solar radiation at the top of the 
atmosphere determined using the method described by Robertson and Russelo 
(1968). Both equations had an r 2 value exceeding 0.99. 

LE values from equation (#) were converted to total PE in mm from June 
through August by the formula 

Total PE = LE x 0.086 x N (11) 

where N is the total number of days in the period. 



For convenience, the drying index I was normalized to a maximum of 100 
by the following formula : 

I N = I_x 100 (12) 

where Ijj is the normalized index; 

I is the original drying index calculated from Equation (7); and 
I-MAX i- s the maximum value of the drying index, taken as 360 mm. 

Water deficit zonation was accomplished by using modifications of 
water balance procedures described in detail by Thornthwaite (1948) and 
Thornthwaite and Mather (1957). Thornthwaite defined moisture deficit as 
the amount by which potential exceeds actual evapotranspiration in any 
month. Calculations are time consuming and require knowledge of the soil 
water holding capacity (WHC). 

In this study, water deficits were calculated for three WHC's (50, 100 
and 200 mm) using relationships between seasonal water deficits and 
Accumulated Potential Water Loss (APWL) shown in Figure 3. Thornthwaite 
and Mather (1957) defined APWL as the sum of all negative monthly values 
of P-PE. In this study, APWL is defined as the sum of all positive values 
of PE-P for convenience. The relationships in Figure 3 were based on 
Thornthwaite water balance tabulations for selected stations in the 
Atlantic provinces and Ontario by Phillips (1976). However, Phillips only 
calculated water deficits for 100 and 200 mm WHC. The graph for 50 mm WHC 
was constructed by calculating water deficits following Thornthwaite 's 
procedures (Thornthwaite and Mather, 1957). 

APWL's were calculated for 232 climate stations in the region using 
total precipitation and PE values for the months of June through August 
for the 1951-1980 normal period (Environment Canada, 1982). This 
procedure was valid since in most cases, PE-P was positive or near zero 
for these months only. PE was estimated by the same procedure as 
previously described for the drying index, rather than by the Thornthwaite 
method. Thornthwaite 1 s procedure overestimated PE in coastal areas of the 
Atlantic region because it is based on mean temperature and does not 
account for differences in relative humidity or vapour pressure deficit. 
The formula of Baier and Robertson (1965) accounts for humidity 
differences to some extent, since coastal areas with mean temperatures 
comparable to inland locations have lower PE values due to smaller 
day /night temperature ranges. PE estimates using the Baier and Robertson 
formula were as much as 20 per cent higher than Thornthwaite PE for some 
stations. For this reason, data from selected stations in Ontario 
(Phillips, 1976) were used to determine the relationship between APWL and 
water deficits in Figure 3 at these higher PE values. 

Water deficits were calculated using equations fitted to the graphs in 
Figure 3. Best results were achieved by using two equations for each of 
the curves as shown in Table 2. 




WATER DEFICIT (mm) 



Table 2. Equations for calculating water deficits (WD) from Accumulated 
Potential Water Loss (APWL) 



WHC x APWL d 

(mm) range Equation used to estimate water deficits 



(mm) 



50 0-70 WD= 0.404 + 0.11351 AWPL + 0.005220 (APWL) 2 

50 >70 WD= -16.658 + 0.6520 APWL + 0.0010685 (APWL) 2 

100 0-150 WD = 0.01697 ( APWL) 1 ' 67581 

100 >150 WD = 0.85338 APWL - 52.776 

200 0-150 WD = 0.0061224 (APWL) 1,78276 

200 >150 WD = 0.61737 APWL - 46.222 



1 WHC - water holding capacity of the soil. 

2 APWL - accumulated potential water loss. 
NOTE: For APWL ^0.0, WD = 0.0. 

2.5 Mapping procedures 

Criteria previously described were determined for approximately 232 
climatic stations in the Atlantic region. Results were plotted on maps of 
the region and isolines connecting points of equal value were drawn. Major 
topographic features such as the Annapolis and Saint John River valleys 
were considered when drawing isolines. Data from climate stations in 
Quebec and Maine were used to help position isolines of the criteria 
described in sections 2.1, 2.2 and 2.3 in the vicinity of the borders. 
Adjustments were also made to account for biases in these same criteria at 
first order hourly synoptic stations in the region. These biases are due 
to different observational procedures with respect to the climatological 
day for minimum temperature at synoptic and ordinary climate stations 
(Bootsma, 1976). For example, a bias in the monthly mean air temperature 
at stations with hourly observations could delay estimated spring maturity 
dates (section 2.1) by as much as 5 days. Where discrepancies were 
evident, more weight was given to ordinary climate stations than to first 
order stations in the mapping procedure. 



3. RESULTS AND DISCUSSION 

A general map of the Atlantic region which identifies the locations 
referred to in the text is shown in Figure 4. The province of Newfoundland 
was mapped at a considerably smaller scale than the other three Maritime 
provinces. A list of climatic stations used in this study and calculated 
values for designated criteria are given in the Appendix. The approximate 
locations of the climatic stations are identified in the Appendix in Figure 
10. 



13 




3.1 Heat unit zonation for estimating optimum first harvest date 

Since isoline patterns for the dates when 350 GDD and 450 GDD have 
accumulated in spring as determined from equations (1) and (2) were 
similar, one zonation map could be drawn for the region (Figure 5). The 
450 GDD date was generally 10 days later than the 350 GDD date. The 
average dates when 350, MOO and 450 GDD have accumulated in each zone in 
Figure 5 are given in Table 3. The 400 GDD dates were derived by 
interpolation. 

The date when 350 GDD have accumulated in spring varied from before 
June 15 in the Annapolis and Saint John River valleys to as late as the 
last week in July in some parts of Newfoundland. The 350 GDD date 
corresponds to the date when Saranac and Iroquois alfalfa are estimated to 
reach the early bud stage in an average year in each region. This 
represents the earliest possible date for the first cut if a maximum period 
of regrowth is desired for additional harvests later in the season. 
Alfalfa cut on this date would have higher digestibility and protein 
content than if cut at 450 GDD, but lower dry matter yields (Atlantic Field 
Crops Committee, 1980). Clair timothy is also expected to be at the 
desirable maturity stage for first cut on this date. 

The date when 450 GDD have accumulated in spring varies from before 
June 25 in the Annapolis and Saint John River valleys, to as late as the 
first week in August in some areas of Newfoundland. This date corresponds 
approximately to the optimum date of first cutting of Climax timothy and 
double cut red clover cultivars, and the latest desirable cutting date of 
alfalfa. 

The data presented are based on expected heat unit accumulations in a 
normal year. Variation in maturity will occur from season to season 
depending on weather conditions. Within each zone there will also be 
variability in heat units available to the crop due to differences in soil 
and in microclimate. For example, forages grown on cool, wet soils which 
are slow to warm up in spring will mature later than those grown on warmer 
soils although yields may be higher on the former. Field exposure will 
also affect the accumulation of heat units, and good shelter due to 
windbreaks and/or topography can advance maturity considerably. Weather 
stations are usually located on fairly well-exposed sites and the zonation 
map should be quite representative of this type of condition. The map 
should be helpful in formulating recommendations on suitable harvesting 
dates for the first cut of forage crops in each area of the Atlantic 
region. However, growers will need to base their decision on when to 
actually take the first cut on the observed stage of maturity as it is 
influenced by local environmental conditions and management. 



16 

Table 3. Average dates of accumulated growing degree-days (GDD) for 
maturity zones in Figure 5 



Zone 




Average da' 


tes when GDD have 


accumulated 




35C 


) GDD* 1 




400 GDD* 2 




450 GDD*3 


Ml 


June 


15 or 


earlier 


June 21 or earl: 


ier 


June 25 or earlier 


M2 


June 


16-20 




June 22-26 




June 2 6-30 


M3 


June 


21-25 




June 27-Jul 1 




July 1-5 


M4 


June 


26-30 




July 2-6 




July 6-10 


M5 


July 


1-5 




July 7-11 




July 11-15 


M6 


July 


6-15 




July 12-21 




July 16-2 5 


M7 


July 


16-25 




July 22-31 




July 2 6- Aug 4 


M8 


July 


26 or 


later 


Aug 1 or later 




Aug 5 or later 



Estimated average date when alfalfa in early bud and Clair timothy 
in early head stage. 

Estimated average date when alfalfa in late bud stage, Clair 
timothy in 50% head and Champ timothy in early head stage. 
Estimated average date when alfalfa and double cut red clover in 
early bloom, Champ timothy in 50$ head and Climax timothy in early 
head stage. 

Note: Alfalfa refers to the cultivars Saranac and Iroquois; 

red clover refers to the cultivars Lakeland and Ottawa. 



3.2 Critical fall harvest period for alfalfa 

The average date when 450 GDD remain in the fall as determined by 
equations (4) and (6) was used to construct the zonation map shown in 
Figure 6. Since the 450 GDD date was taken as the beginning of a 45-day 
period during which alfalfa should not be harvested, it was possible to 
define a critical fall harvest period for each zone as shown in Table 4. 
The estimated starting date of the critical period ranged from as early as 
August 5 in northwestern New Brunswick to as late as September 5 in some of 
the coastal regions in southwestern Nova Scotia. In most of the 
agricultural areas within the region, the estimated starting dates ranged 
between August 21 and September 4 (zones F5 to F7). In Labrador, the date 
when 450 GDD remain in fall ranged from as early as July 10 in the north to 
after July 25 in the southeast. 



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Variations in the critical harvest period within each zone are likely, 
depending upon local conditions of shelter and frost. Seasonal weather 
patterns can also cause some shifts in the critical period from year to 
year within a particular zone, although such variation is not likely to be 
large (Fulkerson, 1970). 

Table 4. Critical fall harvest period for alfalfa for zones in Figure 6 



Zone Critical Fall Harvest Period 

Start of period 1 End of period * 2 

Fl Aug. 5 or earlier Sept. 20 or earlier 

F2 Aug. 6-10 Sept. 21-25 

F3 Aug. 11-15 Sept. 26-30 

F4 Aug. 16-20 Oct. 1-5 

F5 Aug. 21-25 Oct. 6-10 

F6 Aug. 26-30 Oct. 11-15 

F7 Aug. 31-Sept. 4 Oct. 16-20 

F8 Sept. 5 or later Oct. 21 or later 



Based on date when 450 GDD are remaining in the fall. 
Based on 45 days after the starting date. 



In areas of the region where alfalfa production is feasible, it is best 
not to harvest alfalfa during the critical period indicated by the zonation 
map as this prevents the plants from reaching adequate hardiness before 
entering the dormant stage (Fulkerson, 1970). Harvesting around the middle 
of the critical period results in the most damage since this will cause 
plants to enter dormancy with the lowest levels of food reserves 
(Fulkerson, 1974). Harvesting before the critical period allows the plants 
to enter later growth stages during which it develops buds on basal stems 
and crowns and begins to store sufficient food reserves in the roots. 
These buds must be well protected during winter, as the number of survived 
buds determines the number of new shoots in the spring. Added protection 
can be provided to the buds by leaving the fall growth to act as a 
windbreak and catch the snow over the winter. If winterkill of alfalfa is 
not a problem, the critical harvest period could possibly be shortened 
somewhat at either end without causing a significant decline in survival. 
However, this would have to be determined by experience within a local area. 



The zonation map should be helpful in formulating recommendations on 
harvest management of alfalfa in late summer and fall. Following the 
suggested cutting practices does not guarantee good survival, but will 
assist in reducing the risk of winter injury. The zonation map may also be 
useful for other crop species that are subject to winterkill and that 
require a fall rest period. For example, experimental data from Ontario 
have indicated that birdsfoot trefoil also requires a fall rest period, 
although the critical fall harvest date when most damage is sustained may 
be more than a week earlier than for alfalfa (Fulkerson, 1982). Other 
species to which this zonation may apply include clover and less hardy 
grass species such as orchardgrass and perennial ryegrass. 

3.3 Zones for harvest frequency and potential yield 

The variation in the index of growing season length (DAYS) in the 
region is demonstrated by the zonation map in Figure 7. The range in 
values of this index associated with each zone is shown in Table 5. This 
index exceeds 75 days in part of the Saint John River Valley, in the 
Annapolis Valley, and in part of the north shore of Nova Scotia. Most of 
the remainder of the major agricultural regions in the Maritimes fall in 
the H2 zone which has between 60 and 74 days. In Newfoundland, the index 
DAYS ranges from less than zero in the extreme north to over 45 days in the 
Humber Valley region, the Grand Falls-Gander Lake area, and in the vicinity 
of St. John's. In Labrador the date when 350 GDD have accumulated in 
spring generally falls 10 to 30 days after the date when 450 GDD remain in 
autumn. 



Table 5. Growing season length criterion for zones in Figure 7 







Zone 


Days* 


H4 


39-20 


H5 


19-0 


H6 


less than 



* In addition to indicated number of days, there are 350 GDD 
in spring and 450 GDD in fall available for crop growth. 

Results from regional variety trials conducted from 1971 to 1981 by the 
Advisory Committee on Forage Crops (formerly the Forage Sub-Committee of 
the Atlantic Field Crops Committee) and from field experiments on forage 
management by Kunelius et al. (1976, 1977b, 1978, 1980) and by MacLeod et 
al. (1972) were examined to assess potential yields and optimum harvest 



21 

frequencies within specific zones in the region. Since field trials were 
conducted in only three of the six zones, the proposed guidelines are 
somewhat speculative and need to be verified or adjusted as more 
information becomes available from field trials or farming experience. 
Data on red clover were particularly scarce due to difficulties in 
achieving adequate winter survival within experimental plots in many 
years. Data on orchardgrass were also relatively few in comparison with 
most other forage crop species. 

Tables 6 and 7 list estimated optimum harvest frequencies and potential 
yields, respectively, in each zone in Figure 7 for several forage species 
grown in the region. Potential yields are yields which should be 
achievable with good management under present technology. Yield estimates 
are based on yields recorded in field trials conducted at research stations 
in years with relatively good winter survival. Overwintering damage can 
seriously reduce yields of alfalfa, clover and orchardgrass in some years, 
thus making it difficult to achieve potential yields consistently year 
after year. The proposed cutting frequencies attempt to balance quality 
and yield. More frequent harvests will often improve forage quality but 
result in a decline in yield or persistence. 



Table 6. Estimated optimum harvesting frequencies of several 
forage species for each zone in Figure 7 



Forage species Optimum harvesting frequency 

HI H2 H3 H4 H5 H6 



Annual ryegrass * 4 

Alfalfa 3 

Orchardgrass 4-3 

Timothy & brome grass 2 

Red clover 2 



4-3 


3-2 


2 


2-1 


" 


3-2 


2 


1 


1-0 


- 


4-3 


3 


2 


1 


1 


2 


2 


2 


1 


1 


2 


2-1 


1 


1-0 


_ 



■1 



Cutting frequency in seeding year; all others in post- 
seeding years. 
Double cut cultivars such as Ottawa and Lakeland. 



As indicated in Table 6, the optimum cutting frequency for annual 
ryegrass in the most favourable production zones HI and H2 is four times 
(Kunelius, 1980; Kunelius and Calder, 1978) but up to five cuts are 
feasible. Potential yields range from about 8 tonnes dry matter per 
hectare in the more favourable production areas to less than 5 



Table 7. Estimated average potential dry matter yields of several 
forage species for each zone in Figure 7 



Forage 




Average 


potentia 


1 dry 


matter 


yield (t 


n. \*1 

Dnnes/ha) 


species 


HI 


H2 


H3 


H4 


H5 


H6 


Annual ryegra 


ss*2 


8.0 


8.0 


7.0 


5.0 


3.0 


- 


Alfalfa 




8.5 


8.5 


8.5 


6.5 


4.0 


- 


Orchard grass 




7.0 


7.5 


6.5 


5.5 


4.0 


3.5 


Brome grass 




7.5 


8.0 


7.0 


6.0 


5.0 


4.0 


Timothy 




8.5 


9.0 


9.0 


8.0 


6.0 


5.0 


Red clover*3 




8.0 


8.5 


7.5 


6.0 


4.0 


- 



1 Yields are based on assumption that cutting frequencies are 

similar to those listed in Table 6. 
^ Yields in seeding year; all others in post-seeding years. 
*3 Double cut cultivars such as Ottawa and Lakeland. 



tonnes per hectare in zones with shorter growing seasons. One reason why 
annual ryegrass is becoming popular in the region is because of its ability 
to supply quality forage for livestock in late fall when most perennial 
grasses are unproductive (Kunelius, 1980; Kunelius and Calder, 1978). 

The suggested cutting frequencies for alfalfa are based on the 
assumption that at least 40 days are required for regrowth after the first 
cut and prior to the fall rest period when harvesting must be avoided. 
Thus only one cut is feasible in zone H4 while two cuts can be harvested in 
zone H3. In zones Hi and H2 there is a possibility of two additional 
harvests before the fall rest period. These guidelines for harvesting 
frequency are general and need to be modified according to local 
experience. For example, if persistence or winter survival is poor, the 
number of cuts may need to be reduced, while an extra harvest may be 
feasible late in the fall following the critical harvest period if 
winterkill is not a problem (MacLeod et al., 1972). Fewer harvests may 
give better results in years when growth is restricted by abnormally cool 
temperatures or lack of moisture. In the most favourable production areas 
(zones HI, H2 and H3) average yields of 8.5 tonnes dry matter per hectare 
are feasible under good management, normal climate, and good winter 
survival (Table 7). In zones H4 and H5 potential yields are depressed 
partly because only one harvest can be taken. 



23 

Orchardgrass is a fast growing cool season perennial which can be 
harvested 3 or H times per season in the most favourable areas for 
production in the region (Kunelius and Suzuki, 1977b). However, it is 
susceptible to winterkill and may require a long fall rest period similar 
to alfalfa (Kunelius and Suzuki, 1977a). If winter survival is less than 
adequate, the number of cuts may need to be reduced from those indicated in 
Table 6. Average yields of 7 tonnes dry matter per hectare or more are 
achievable in the more favourable production areas (zones HI and H2) while 
yields are limited by cool short growing seasons in zones H5 and H6. 

Timothy is the main forage species used in the region and is capable of 
producing 8 tonnes dry matter per hectare or more in zones HI to H4 with 
good management. Two cuts are feasible in these zones. More frequent 
cutting reduces yields but produces higher quality forage (Kunelius et al. , 
1976) . Bromegrass is noted for its strong second growth and superior 
performance under dry conditions in comparison to timothy, although it is 
somewhat less hardy. Two cuts are possible except in the zones with the 
shortest growing season (H5 and H6). 

Two cuts of red clover are feasible in zones HI to H3 if early- 
flowering cultivars such as Lakeland and Ottawa are grown. In zones H4 and 
H5 only one cut is feasible due to shorter growing seasons. Field trial 
data indicate that the second cut usually can be taken after 50 days or 
more of regrowth. Red clover yields of 8.0 tonnes dry matter per hectare 
can be achieved in the more favourable climatic zones. However, red clover 
is a short-lived legume which is frequently winterkilled and therefore is 
most useful in short-term rotations (Atlantic Field Crops Committee, 
1980) . It is also more difficult to field cure as hay than most other 
forage species. 

The general guidelines on cutting frequencies and potential yields 
apply to near average weather conditions. Abnormal weather conditions in 
any given year can affect the optimum cutting frequency and yield of most 
species. In most cases the final decision on cutting frequency must be 
reached by considering a number of factors including quality, yield, stand 
persistence, winter survival, seasonal weather conditions, and storage 
method (hay or silage) . 

The proposed zonation map (Figure 7) will be useful in formulating 
recommendations on cutting frequencies and potential yields of forage crops 
in various parts of the region. Further improvements in this zonation 
scheme are required which take into greater consideration the influence of 
factors such as winter survival, available moisture and forage quality on 
optimum harvesting frequencies and potential yields. 



3.4 Drying index and water deficit zonation 

A zonation map indicating relative drying conditions for making hay in 
the region is shown in Figure 8. Zone boundaries were determined by 
arbitrarily selected values of the normalized drying index as indicated in 
Table 8. This table also shows the range in the drying index itself and 



24 



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gives a qualitative rating of haymaking conditions for each zone. A more 
detailed analysis of hay-drying conditions in relation to the climate in 
each zone is needed for' a more quantitative assessment of hay-drying 
potential. However, the present map provides a good relative indication of 
drying conditions in the region. 

The best drying conditions are found in zone Dl which has a normalized 
index of 90, and an actual drying index value of 325 mm. This zone is 
found along a large part of the Saint John River valley and stretches into 
a large section of eastern New Brunswick. The zone is also present in 
several regions of Nova Scotia, including part of the Annapolis Valley, an 
area south of Truro and a portion of the north shore region, which 
represent the main farming areas of this province. Prince Edward Island is 
predominantly zone D3, with a normalized index between 65 and 80. Less 
favourable drying conditions in that province are not from higher rainfall, 
but because of lower PE due to depressed daytime temperatures and higher 
humidities. Lower drying potential in much of Newfoundland, most of which 
falls in zones D3 to D5, is similarly more due to lower PE values than to 
higher rainfall. 

In comparison to PE, average rainfall is relatively uniform throughout 
the Atlantic region for the period June-August. Most of the region 
receives an average of 230 and 280 mm of rainfall over the 3-month period, 
while PE ranges from below 250 mm to over 400 mm. 



Range in drying indices for zones in Figure 



Map Drying Normalized 
Zone Index (mm) Index* 



Description of haymaking 
Conditions 



325 



Fair-good (most favourable field 
drying conditions in the region) 



D2 


290-325 


80-90 


Fair 


D3 


235-290 


65-80 


Fair-poor 


D4 


180-235 


50-65 


Poor 


D5 


180 


50 


Very poor 



Very poor (lowest potential for 
field drying in the region) 



*Normalized Index = Drying Index x 100, where Max. Drying 
Max. Drying Index Index is 360 mm. 



The zonation map provides a good indication of the relative drying 
conditions in the region and should be useful for making recommendations on 
harvesting and conservation methods when combined with additional 
information on hay-making conditions in each zone. Further studies to 
quantify the relationship between climate and hay-drying potential in each 
zone would be of benefit in this regard. Variation in drying rates for 
hay-making among crop species needs to be considered in the application of 
a drying zonation system. 



A zonation map for water deficits is shown in Figure 9. Ranges in 
water deficits and APWL values in each of the 5 zones used are shown in 
Table 9. The zone boundaries were selected on the basis of 25 mm intervals 
in water deficits for soils with 100 mm WHC. Water deficits for 50 mm and 
200 mm WHC's are also shown in the table. 

Table 9 indicates that forage crops grown in areas zoned W4 and W5 can 
experience significant water deficits if soils have less than 100 mm WHC. 
However, in zones Wl and W2, even shallow rooted crops like timothy are 
unlikely to experience significant water stress in an average year. 



Table 9. 



Range in Accumulated Potential Water Loss (APWL) and 
water deficits for zones in Figure 9 



APWL 
Water Deficit range 
Zone (mm) 



Approximate water deficit range (mm) 

Soil water holding capacity (WHC) 
50 mm 100 mm 200 mm 



Wl 





W2 


0-78 


W3 


78-116 


W4 


116-150 


W5 


150 



nil nil 

0-40 0-25 

140-75 25-50 

75-105 50-75 

105 75 



nil 
0-15 
15-30 
30-45 
45 



According to Figure 9, under similar soil conditions (ie. WHC and 
drainage) forage crops are most likely to be affected by water stress in 
part of the lower Saint John River valley and eastern regions of New 
Brunswick, and in the Annapolis Valley and part of the north shore regions 
of Nova Scotia. However, these regions are least likely to be affected by 
problems relating to waterlogging of soils, leaching of nutrients and 
denitrification during summer months under given soil conditions. 



27 




28 

Areas zoned Wl or W2 are least likely to experience significant water 
stress, while the probabilities of moisture surpluses which may cause 
excessive leaching and denitrification are the greatest. In New Brunswick, 
zones Wl and W2 are found in the extreme northwest region and along the 
southern coast bordering the Bay of Fundy. In Nova Scotia, these zones are 
mainly confined to areas along the southern and western coast and to areas 
in Cape Breton Island. Most of Newfoundland is in zones Wl and W2, with 
the exception of a few isolated regions. In zone Wl, APWL values are less 
than zero, indicating that rainfall exceeds PE even during the summer 
months. 

It is useful to compare these estimates of Thornthwaite water deficits 
with irrigation requirements or water deficits calculated by Coligado et 
al., (1968) who used a daily water budgeting technique described by Baier 
and Russelo (1968). Average water deficits in this study for soils with 
200 mm WHC were comparable to those by Coligado et al. (1968) at a storage 
capacity of 100 mm (4 inches), a consumptive use factor (CU) between 1.0 
and 0.75 and a risk level of 50 percent. Water deficits for 100 mm WHC 
were similar to Coligado 's at a storage capacity of 50 mm (2 inches) and a 
CU factor of 0.75. Water deficits for soils with 50 mm WHC were comparable 
to Coligado 's at a storage capacity of 25 mm (1 inch) and CU factor 
between 0.75 and 0.5. Since storage capacity as used by Coligado et al. 
(1968) is equivalent to 50 percent of WHC used in this study, the water 
deficits determined by these two methods are remarkably similar. 

Sly and Coligado (1974) developed a simple method for computing 
seasonal water deficits which was used to prepare agroclimatic maps of 
Canada. A soil climate classification system was subsequently designed for 
Canada on the basis of seasonal water deficits (Baier and Mack, 1973; 
Clayton et al., 1977; Mack, 1970). Water deficit zones in this study are 
compared with the moisture subclasses used in the soil climate map of 
Canada in Table 10, thus linking the results to a nationally accepted 
classification system. This comparison provides a means of linking water 
deficits determined by the Thornthwaite approach to the Canadian soil 
climate classification system in the Atlantic region. A qualitative 
description of the moisture stress likely experienced for timothy and 
alfalfa in each zone is also presented in Table 10. 

Irrigation requirements or water deficits computed by Sly and Coligado 
(1974) assume that when the readily available water (50 percent of WHC) 
stored in the soil is depleted, the additional water required is added by 
irrigation. Since forages are produced under non-irrigated conditions in 
the Atlantic region, the Thornthwaite procedure was considered more 
applicable to this study. The present study uses data from more climatic 
stations in the region and from the most recent 30-year normal period. In 
spite of differences in methods and analyses period, the present results 
appear to be relatively compatible with results from previous water deficit 
zonation studies of the region. 

The precise extent to which water deficits limit forage yields in each 
zone is presently not known. Further research is required to help 
determine these relationships and thereby assist in rating land for forage 



29 





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30 

production potential and in evaluating yield response to irrigation. 
Variations in characteristics such as water use, drought resistance and 
resistance to waterlogging among crop species need to be taken into 
consideration in the application of water deficit zonation systems. 



4. CONCLUSION 

The results of climatic analyses presented here will be useful for 
formulating more specific recommendations on production and management of 
forage crops in the Atlantic region. However, available experience in crop 
production in each part of the region will also need to be considered. The 
zonation is on a scale which does not account for variations in crop 
response within zones resulting from differences in micro-climatic 
conditions. Variations in climate between years which influence the 
production and management of forage crops was also not taken into 
consideration in this study. It should be noted that the transition 
between zones on the maps is usually gradual and not abrupt as may be 
implied. 

The criteria used and the interpretations applied will require 
improvement and adjustment as additional information on forage crop 
production and management becomes available from research trials and field 
experience and as existing climatic resources within the region are better 
defined. The results should not be interpreted as a recommendation that 
the species and cultivars referred to are well adapted to all zones in the 
region. Rather, the study provided guidelines on applicable management 
practices if local experience has found production of specific cultivars to 
be feasible. 

Simple procedures for calculating climatic criteria used in zonation 
are described which make use of monthly climatic normals. These facilitate 
the use of data from stations with relatively short term normals which have 
been adjusted to the latest 30-year normal period. The procedures also 
simplify calculations for other normal periods as may be required. Several 
areas requiring additional research have been identified. The zonation 
maps should be helpful in selecting suitable locations for conducting field 
experiments. Finally, the results of this study have significance for land 
evaluation, particularly when integrated with information on soils in the 
region. 



31 

5. REFERENCES 

Atlantic Field Crops Committee. 1975. Report of field trials conducted 
in 1975. Forage Sub-Comm. Report, p. G-6. 

Atlantic Field Crops Committee. 1980. Field crop guide, Atlantic 
provinces. A.F.C.C. Publ. 100, Agdex 100, pp. 33-45. 

Baier, W. 1971. Evaluation of latent evaporation estimates and their 

conversion to potential evaporation. Can. J. Plant Sci. 51: 
255-266. 

Baier, W. and Mack, A.R. 1973- Development of soil temperature and soil 

water criteria for characterizing soil climates in Canada. In: Field 

Soil Water Regimes, special publ. No. 5, Soil Sci. Soc. Amer. , p. 
195-212. 

Baier, W. and Robertson, G.W. 1965. Estimation of latent evaporation 
from simple weather observations. Can. J. Plant Sci. 45:276-284. 

Baier, W. and Russelo, D.A. 19 68. A computer program for estimating 

risks of irrigation requirements from climatic data. Tech. Bull. No. 
59, Agrometeorol. Sect., Plant Res. Inst., Can. Dept. Agric. , Ottawa, 
48 pp. 

Black, W.N. 1978. Effects of irrigation and nitrogen on a natural 
pasture sward. Can. J. Plant Sci. 58: 347-356. 

Bootsma, A. 1976. A note on minimum temperature and the climatological 
day at first order stations. Atmosphere 14(1): 53-55. 

Calder, F.W. and Nicholson, J.W.G. 1970. Pasture productivity of three 
swards with and without nitrogen fertilizer. Can. J. Anim. Sci. 50: 
467-473. 

Clayton, J.S., Ehrlich, W.A., Cann, D.B., Day, J.H. and Marshall, I.B. 
1977. Soils of Canada, Vol. 1: Soil Report, p. 73-77. 

Coligado, M.C., Baier, W. and Sly, W.K. 1968. Risk analyses of weekly 

climatic data for agricultural and irrigation planning. Tech. Bull. 
Nos. 17-24, Agrometeorol. Sect., Plant Res. Inst., Can. Dep. Agric, 
34 pp. 

Environment Canada. 1971. Temperature and precipitation 1941-1970, 

Atlantic provinces. Atmospheric Environment Service, Downsview, 
Ont. , 55 pp. 



32 

Environment Canada. 1982. Canadian climate normals: temperature and 

precipitation 1951-1980, Atlantic provinces. Atmospheric Environment 
Service, Downsview, Ont., 136 pp. 

Fulkerson, R.S. 1970. Location and fall harvest effects in Ontario on 

food reserve storage in alfalfa (Medicago sativa L. ) . In: 
Proceedings of the XI International Grassland Congress, Univ. 
Queensland Press, p. 555-559. 

Fulkerson, R.S. 1974. Stop alfalfa winterkill. Ontario Min. Agric. 
Food, Factsheet #74-040, Agdex 121/21, 2 pp. 

Fulkerson, R.S. 1982. Fall harvest effects on the yield and persistence 
of birdsfoot trefoil ( Lotus corniculatus L. ) Forage Notes 26(1):12-13. 

Gottfred, N. 1980. Winter survival of forage stands. Manitoba 
Agriculture, Forage Facts, Agdex 120/21, 3 pp. 

Grant, E.A. and Burgess, P.L. 1978. Timothy: High-quality forage for 
livestock in Eastern Canada. Agriculture Canada publ. 1640, 15 pp. 

Hayhoe, H.N. and Jackson, L.P. 1974. Weather effects on hay drying 
rates. Can. J. Plant Sci. 54: 1479-484. 

Heinrichs, D.H. 1969. Alfalfa in Canada. Canada Dept. Agric. Publ. 
1377, 28 pp. 

Knight, W.E. and Hollowell, E.A. 1958. The influence of temperature and 
photoperiod on growth and flowering of crimson clover ( Trifolium 
incarnatum L. ). Agron. J. 50:295-298. 

Kozumplik, V. and Christie, B.R. 1972. Heading response of orchardgrass 
seedlings to photoperiod and temperature. Can. J. Plant Sci. 52: 
369-373. 

Kunelius, H.T. 1980. Effects of nitrogen rates and harvest schedules on 
yield and quality of Westerwolds ryegrass grown as a summer annual. 
Can. J. Plant Sci. 60: 519-524. 

Kunelius, H.T. , Suzuki, M. and Winter, K.A. 1976. Influence of harvest 

systems and nitrogen rates on yields, quality, and persistence of 
Champ timothy in the seeding and postseeding years. Can. J. Plant 
Sci. 5b: 715-723. 

Kunelius, H.T. and Suzuki, M. 1977a. Seeding year yields and quality of 
orchardgrass as influenced by N rates and harvest systems. Can. J. 
Plant Sci. 57: 427-431. 



33 

Kunelius, H.T. and Suzuki, M. 1977b. Response of orchardgrass to 

multiple harvests and rates of nitrogen in post-seeding years. Can. 
J. Plant Sci. 57: 763-770. 

Kunelius, H.T. and Calder, F.W. 1978. Effects of rates of N and regrowth 
intervals on yields and quality of Italian ryegrass grown as a summer 
annual. Can. J. Plant Sci. 58: 691-697. 

Mack, A. R. 1970. Report of the subcommittee on soil climate in relation 
to soil classification and interpretation. In: Proceedings of the 
eighth meeting of the Canada Soil Survey Committee, Ottawa, Ont., pp. 
21-34. 

MacKenzie, D.N. and Suzuki, M. 1978. Winter survival of forage legumes, 

winter cereals and strawberries in the Maritime provinces in 1978. 

1978 Research Summary, Agric. Can. Res. Sta. , Charlottetown, ip. 
30-31. 

MacLeod, L.B., Kunelius, H.T. and Calder, F.W. 1972. Effects of early 

summer and fall cutting management on dry matter yields, 
digestibility, crude protein, and survival of Saranac and 
Narragansett alfalfas. Can. J. Plant Sci. 52: 941-948. 

Ontario Field Crops Research Committee. 1981. 19 81 Field crop 
recommendations. Ont. Min. Agric. Food, Publ. 296, p. 10. 

Pearson, C.J. and Hunt, L.A. 1972. Effects of temperature on primary 
growth of alfalfa. Can. J. Plant Sci. 52:1007-1015. 

Phillips, D.W. 1976. Monthly water balance tabulations for 

climatological stations in Canada. Environment Canada, Atmospheric 
Environment, DS No. 4-76 (Revised). 

Robertson, G.W. and Russelo, D.A. 1968. Astrometeorological estimator 

for estimating time when sun is at any elevation, elapsed time 
between the same elevations in the morning and afternoon, and hourly 
and daily values of solar energy, Q . Tech. Bull. 14, 
Agrometeorol. Sect. , Research Branch, Agriculture Canada, Ottawa, 22 
pp. 

Selirio, I.S. and Brown, D.M. 1979. Soil moisture-based simulation of 
forage yield. Agric. Meteorol. 20:99-114. 

Sly, W.K. and Coligado, M.C. 1974. Agroclimatic maps for Canada-derived 
data: Moisture and temperature regimes. Tech. Bull. No. 8l, 
Agrometeorol. Sect., Plant Res. Inst., Agric. Canada, Ottawa, 36 pp. 

Smith, D. and Jewiss, O.R. 1966. Effects of temperature and nitrogen 

supply on the growth of timothy (Phleum pratense L.). Ann. Appl. 
Biol. 58: 14 5-157. 



34 

Suzuki, M. and McRae, K.B. 1979. Factors influencing winter survival of 
forage legumes in the Maritime provinces. 1979 Research Summary, 
Agric. Can. Res. Sta., Charlottetown, p. 32. 

Thorn, H.C.S. 1966. Normal degree days above any base by the universal 
truncation coefficient. Monthly Weather Review 94(7): 461-465. 

Thornthwaite, C.W. 1948. An approach towards a rational classification 
of climate. Geographical Review 38(1): 55-94. 

Thornthwaite, C.W. and Mather, J.R. 1957. Instructions and tables for 
computing potential evapotranspiration and the water balance. Drexel 
Inst. Tech., Centerton, N.J., Publ. Climatol. 10(3): 181-311. 

Treidl, R.A. (ed.) 1978. Handbook on agricultural and forest 

meteorology, Part I. Atmospheric Environment Service, Downsview, 
Ont., Table 3- 

Treidl, R.A. (ed.) 1979. Handbook on agricultural and forest 

meteorology, Part II. Atmospheric Environment Service, Downsview, 
Ont., Table 5. 

Wilkinson, J.M. 1981. Losses in the conservation and utilization of 
grass and forage crops. Ann. Appl. Biol., 98: 365-375. 

Willis, C.B. and Suzuki, M. 1971. Effect of cutting management on forage 
yield, carbohydrate reserves and root vitality of alfalfa. 1971 
Research Summary, Agric. Can. Res. Sta., Charlottetown, p. 21-22. 

Woolley , D.G. and Wilsie, C.P. 1961. Cold unit accumulation and cold 
hardiness of alfalfa. Crop Sci. 1: 165-167. 



35 

6. APPENDIX 

Climatic data from 232 stations in the Atlantic region listed in 
Table 11 were used in the forage crop zonation study. A map is supplied 
in this appendix which shows the approximate location of each climate 
station (Fig. 10). Parameters that were derived from station data are 
listed in Table 11. Following is a brief explanation of each parameter 
listed: 

Column 



1. Station number . This number was assigned on the basis of an 
alphabetical listing of stations by province. It corresponds with 
numbers in Fig. 10. 

2. Station name . Station names were taken from published normals for 
the 1951-1980 period by Environment Canada (1982). Where the same 
name is assigned to more than one station, the station elevation is 
given in brackets following the name. 

3- Type of normal . The code for length of record is based on 
temperature and precipitation normals published for the 1951-1980 
period by Environment Canada (1982). Where the normal period for 
these two variables differ, the temperature code is given first, 
followed by the code for precipitation, e.g. 1/2. The codes refer to 
the following periods of record: 



1 complete 30 years 

2 25 to 29 years 

3 20 to 24 years 

8 adjusted normals based on 5 to 19 years inclusive from 
1951 to 1980, and any other available data from 1931 
to 1950 

First order synoptic stations with hourly observations are identified 
with an asterisk (*) following the type of normal. These stations 
may have a bias in any data derived from temperature due to a shift 
in the climatological day for minimum temperature from ordinary 
climate stations. 

4. 450 GDP date in spring . This is the average date when 450 growing 
degree-days above 5°C have accumulated in spring based on regression 
equation (2) using May/ June mean air temperature for the 1951-1980 
normal period. The 350 GDD date is generally about 10 days earlier. 

5. 450 GDD date in fall . This is the average date when 450 growing 
degree-days above 5°C are remaining in fall, as estimated using 
regression equations (4) and (6) and September/October mean air 
temperature for the 1951-1980 normal period. 



36 

6. Days . This represents the index of growing season length as 
determined by the time interval in days between the date when 350 ODD 
have accumulated in spring and when 450 GDD are remaining in the 
fall. 

7. Drying index . The value of the drying index, in mm, is determined 
using equation (7). 

8. Normalized drying index . The values in this column are calculated 
using equation (12). Since it is a "normalized" index, it has no 
units. In a few cases the index value may exceed 100. 

9. PE. The potential evaporation in mm from June through August is 
estimated by the Baier and Robertson method (equations (8) and 
(ID). 

10. Precip . The average total precipitation (P) from June through 
August, in mm, for the 1951-1980 normal period. 

11. APWL. The accumulated potential water loss in mm is determined for 
the period June through August using the formula APWL = PE - P. 

12. Water deficit . The average water deficits (mm) for soils with 50, 
100 and 200 mm water holding capacity are calculated from APWL values 
using equations shown in Table 2. Water holding capacity is here 
defined as the amount of soil water between field capacity and the 
permanent wilting point. 



37 




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CONVERSION FACTORS 








Approximate 








conversion 




Metric units 




factors 


Results in: 


LINEAR 








millimetre (mm) 




X 0.04 


inch 


centimetre (cm) 




X 0.39 


inch 


metre (m) 




X 3.28 


teet 


kilometre (km) 




X 0.62 


mile 


AREA 








square centimetre (cm 2 ) 


X 0.15 


square inch 


square metre (m 2 ) 




X 1.2 


square yards 


square kilometre (km 2 ) 


X 0.39 


square mile 


hectare (ha) 




X 2.5 


acres 


VOLUME 








cubic centimetre (cm 3 ) 


X 006 


cubic inch 


cubic metre (m 3 ) 




X 35.31 


cubic teet 


cubic metre (m 3 ) 




X 1.31 


cubic yards 


CAPACITY 








litre (L) 




■ 035 


cubic toot 


hectolitre (hl_) 




X 22 


gallons 


hectolitre (hL) 




x 25 


bushels 


WEIGHT 








gram (g) 




* 04 


oz avdp 


kilogram (kg) 




> 22 


lb avdp 


tonne (t) 




■ 1 1 


short tons 


AGRICULTURAL 








litres per hectare (L 


ha) 


« 089 


gallons per acre 


litres per hectare (L 


ha) 


< 357 


quarts per acre 


litres per hectare (L 


ha) 


• 071 


pints per acre 


milhlitres per hectare (mL ha) 


• 0014 


II oz per acre 


tonnes per hectare ( 


t ha) 


- 45 


tons per acre 


kilograms per hectare (kg ha) 


• 89 


lb per acre 


grams per hectare (g ha) 


X 0014 


oz avdp per acre 


plants per hectare (plants ha) 


• 405 


plants per acre 



LIBRARY / BIBLIOTHEQUE 



AGRICULTURE CANADA C 

3 1073 000E83 C 10 5